Exhaust gas recirculation system

ABSTRACT

An exhaust gas recirculation system comprising a flow rate control valve provided in the recirculation passage for the exhaust and suction systems of the engine, a diaphragm chamber adapted for controlling the flow rate control valve and arranged to be selectively connected to the suction system and to a pressure amplifier through a pressure change-over valve, and an air bleeding mechanism provided in said pressure amplifier for converting negative pressure variation in the suction system into an amplified positive pressure variation.

United States Patent 11 1 1111 3,877,452 Nohira et al. Apr. 15, 1975EXHAUST GAS RECIRCULATION SYSTEM 3,774,583 11/1973 King 123/119 A3.796049 3 1974 1+ -11" 123 119 A 75 1111761110151 Hidetaka Nohira;Kiyoshi Kobashi, I

both of Susono Japan Primary ExaminerWendell E. Burns [73] Assignee:Toyota Jidosha Kogyo Kabushiki Attorney, Agent, or Firm-Stevens, Davis,Miller &

Kaisha, Toyota, Japan Mosher 22 Filed: Mar. 28, 1974 21 Appl. No.2455,880

[57] ABSTRACT An exhaust gas recirculation system comprising a flow ratecontrol valve provided in the recirculation pas- [30] ForeignApplication Priority Data sage for the exhaust and suction systems ofthe engine, May 24, 1973 111 11111 48-57239 a diaphragm Chamber adaptedfor Controlling the flow rate control valve and arranged to beselectively con- 521 US. Cl 123/119 A nected to the Suction system andto prsssure p 511 111:. CI. P021111 25/06 fier through a Pressurechange-Over valve, and an air [58] Field of Search 123/119 A; 60/278bleeding mechanism Provided in Said Pressure p fier for convertingnegative pressure variation in the [56] 7 References Cited suctionsystem into an amplified positive pressure vari- UNITED STATES PATENTS3,739,797 6/1973 Caldwell 123 119 A 3 laims, 7 Drawing Figures I I 85 981| 1 l 3 ll 1 l 88 2 J 7| l 7 1 I00 l 99 97 22 2| l l l l l lPATENTEDAPR 1 51975 sumaqr'g EXHAUST GAS RECIRCULATION SYSTEM BACKGROUNDOF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to anexhaust gas recirculation system in which a variable weak negativepressure in the suction system of an internal combustion engine isconverted into a proportional strong positive pressure by a pressureamplifier so as to open or close the exhaust gas flow rate control valvein the recirculation system with said positive pressure.

2. DESCRIPTION OF THE PRIOR ART In most of the existing exhaust gasrecirculation systems for vehicles, the control valve used forcontrolling the recirculation rate of exhaust gas is controlled by apressure signal, and usually a diaphragm type valve is used for thecontrol valve because such diaphragm type valve provides a relativelylarge valve shaft driving force. Also, negative pressure in a venturi isutilized as a controlling signal for the control valve. This has theadvantage that proper controlling of the recirculation rate of exhaustgas is provided. However, such negative pressure of a venturi is alittle too weak to directly actuate the diaphragm of the control valve.There is known a mechanism for amplifying such venturi negative pressurefor use as an energy source. However, such negative pressure amplifyingmechanism has the problem that negative pressure varies frequentlyaccording to the operating condition of the engine as negative pressurein the suction pipe is used as energy source. Therefore, there is used anegative pressure storage tank for constantly obtaining negativepressure signal by amplifying the venturi negative pressure, but thisstill involves the problems that air could leak from the ampli fyingmechanism and that the negative pressure storage tank would prove shortof capacity when negative pressure in the suction pipe is weak. Thus, inorder to meet various operating conditions of the engine, the negativepressure storage tank must be of a fairly large capacity, and loading ofsuch large capacity tank to a passenger vehicle would pose anotherproblem.

SUMMARY OF THE INVENTION The present invention provides an exhaust gasrecirculation system featuring an arrangement by which the exhaust gasflow rate control valve is operated by positive pressure. According tothe recirculation system of the present invention, compressed air isintroduced into a controlled pressure chamber in a pressure amplifierfrom a positive pressure source, and the introduced compressed air isreleased into the atmosphere correspondingly to pressure in saidcontrolled pressure chamber and negative pressure in the vicinity of theventuri in the suction system. There is thus formed a pressureamplifying mechanism producing the same effect as would be obtained whenvariation of negative pressure around the venturi is amplified bypressure in the controlled pressure chamber, and such pressureamplifying mechanism is used to practice positive opening and closing ofthe control valve provided in an exhaust gas recirculation passage.Opening of the control valve is effected by said pressure amplifierwhile closing of the valve is accomplished by negative pressure in thesuction system. Also, the control valve is kept closed according to theoperating condition of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram of aninternal combustion engine adapted with an exhaust gas recirculationsystem of the present invention;

FIG. 2 is a longitudinal sectional view of a pressure amplifier and apressure change-over valve according to the present invention;

FIG. 3 is a longitudinal sectional view of a control valve;

FIG. 4 is a longitudinal sectional view of another control valve;

FIG. 5 is a system diagram of an internal combustion engine adapted withan exhaust gas recirculation system according to another embodiment ofthe present invention;

FIG. 6 is a longitudinal sectional view of a pressure amplifier and acontrol valve in the system of FIG. 5; and

FIG. 7 is a longitudinal sectional view of a pressure change-over valveused in the above system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is nowdescribed in detail by way of an embodiment illustrated in FIGS. 1 to 3of the drawings.

The engine body 1 is provided with an intake manifold 2 and an exhaustmanifold 3. The fuel-air mixture is supplied into said intake manifold 2through an air cleaner 4, a venturi 5 in the carburetor and a throttlevalve 6, and exhaust gas is discharged out from the engine 1 into theatmosphere through said exhaust manifold 3. Said exhaust mainfold 3 andintake manifold 2 are connected to each other by a conduit 8 providedwith a control valve 7 at a suitable location thereof so that a portionof exhaust gas will be guided back into the intake manifold 2. In thebody portion 51 of said control valve 7 is provided a passage 52 forpassing exhaust gas, and in said passage 52 is provided a fixed orifice54 which is opened or closed by a valve 53. Disposed above said valvebody 51 is a housing provided with two diaphragms 58 and 59 of differentsizes defining in said housing an atmospheric pressure chamber 55, acontrolled pressure chamber 56 and an atmospheric pressure chamber 57successively in that order upwardly. Between said two diaphragms 58 and59 is provided a strut 61 adapted for maintaining a constant distancetherebetween, and in the atmospheric pressure chamber 57 is provided aspring 62 adapted for pressing the diaphragm 59 toward the controlledpressure chamber 56. The opening-closing valve 53 is joined to the twodiaphragms 58 and 59 by a shaft 64 which extends through a seal 63 ofthe valve body 51 and is arranged to open the fixed throttle 54 when apositive pressure is introduced into the controlled pressure chamber 56from a pressure amplifier 11 which is described later. The control valve7 may also be arranged such that the opening-closing valve 53 isprovided upstream of the fixed orifice 54 and the controlled pressurechamber 56 is defined by one diaphragm 65 and housing 66 so that saidvalve 53 will be opened or closed by the operation of said diaphragm 65,as shown in FIG. 4.

The presssure amplifier unit 11 is provided so that a positive pressurecorresponding to negative pressure in the suction system will besupplied into the controlled pressure chamber 56 in the control valve 7.A diaphragm 15 pressed by a spring 14 is provided between a housingportion 12 and another housing portion 13 of said unit 11, said bothhousing portions 12 and 13 being joined by bolts 16 to define acontrolled pressure chamber 17 on the housing portion 12 side and anatmospheric pressure chamber 18 communicated with the atmosphere on thehousing portion 13 side. In the housing portion 12 is provided a conduit20 having a orifice 19, said pipe 20 being connected to an engine-drivenair pump 21 and a conduit 22 so that a positive pressure will besupplied into the controlled pressure chamber 17. Also provided in saidhousing portion 12 is a pressure outlet port 23' which is communicatedwith an inlet port 24 of a pressure change-over valve 41 to be describedlater, said valve 41 being further communicated with the controlledpressure chamber 56 in the control valve 7 through a conduit 71 so thata positive pressure controlled by the pressure amplifier unit 11 will beselectively supplied to the control valve 7. A hole 25 is formed in thediaphragm 15 in the pressure amplifier unit 11, and an air bleedingportion 26 is provided in said hole on its side closer to theatmospheric pressure chamber 18. Said air bleeding portion 26 has ableeding hole 27 for discharging positive pressure into the atmosphericpressure chamber 18, and a check ball 29 pressed by a spring 28 ispositioned in said bleeding hole 27. Disposed above and joined integralto said housing portion 13 are another housing portion 33 and adiaphragm 32 pressed by a spring 31. Defined by said diaphragm 32 andsaid housing portion 33 is a negative pressure chamber 35 into whichnegative pressure is introduced through the conduit 36 provided in thehousing portion 33 which communicates with a section near the venturi ofthe carburetor by a conduit 37. The pressing force of the spring 31 isadjusted by an adjusting screw 38 to regulate the position of thediaphragm 32. Joined to the underside of the diaphragm 32 and secured bya nut 40 is a stick 39 against which the check ball 29 in the airbleeding portion 26 is pressed against the force of spring 28corresponding to the positions of said diaphragms and 32. The pressingforce of the respective springs 14 and 31 and position of the airbleeding portion 26 are suitably regulated so that the distances ofmovement of said both diaphragms 15 and 32 will be equal to each other.That is, when negative pressure in the negative pressure chamber 35 ofthe pressure amplifier unit 11 is strong, the diaphragm 32 is raised upagainst the force of the spring 31 to let the stick 39 separate from thecheck ball 29 so that the bleeding hole 27 is closed by the check ball29. Therefore, pressure in the controlled pressure chamber 17 isintensified by the air pump 21, causing the diaphragm 15 to rise up withthe air bleeding portion 26. However, if said diaphragm 15 rises up toomuch, the check ball 29 is forced down by the stick 29 so that positivepressure in the controlled pressure chamber 17 is released out throughthe bleeding hole 27, and consequently, pressure in said controlledpressure chamber 17 is weakened to let the diaphragm 15 descend. If saiddiaphragm descends too much, the

bleeding hole 27 is closed by the check ball 29 as said pressure chamber35. This may be expressed by the following formula:

[N THE ABOVE FORMULA:

S effective area of diaphragm 32; S effective area of diaphragm 15; Pnegative pressure in negative pressure chamber 35; P positive pressurein controlled pressure chamber 17; P initial setting value of negativepressure in negative pressure chamber 35; P initial setting value ofpositive pressure in controlled pressure chamber 17; x: diplacement ofdiaphragm 32; y: displacement of diaphragm 15; K spring constnat 31; Kspring constant 14; a proportional constant (amplification rate).(Diaphragm displacement is effected such that x y). A pressurechange-over valve 41 is provided integral with the pressure amplifierunit 11 so that a controlled positive pressure in the pressure amplifierunit 11 will be selectively supplied to the control valve 7. The housing81 of said pressure change-over valve 41 is provided on the side of thehousing portion 12 of said pressure amplifier unit 11 opposite from thecontrolled pressure chamber 17, and the chamber 82 in said housing 81 iscommunicated with the pressure outlet port 23' of the controlledpressure chamber 17 through a valve seat 83. At a location in thechamber 82 opposed to the valve seat 83 is provided another valve seat84 which is connected to a part of the suction pipe 2 positioneddownstream of the throttle valve 6 through a conduit 85. A passage 86provided in the housing 81 is communicated with the controlled pressurechamber 56 by said conduit 71 so that said chamber 82 will be always incommunication with controlled pressure chamber 56 in the control valveassembly 7. On the side of the housing 81 opposite from the pressureamplifier unit 11 is mounted a housing 91 provided with a diaphragm 89defining an atompsheric pressure chamber 87 and a negative pressurechamber 88, and a valve 92 adapted for selectively closing said valveseats 83 and 84 is connected to the diaphragm 89 by a shaft 93 whichextends through the housing 81. Also a seal 94 is provided at the partswhere the shaft 93 passes through the housing 81. in the negativepressure chamber 88 is provided a spring 95 adapted for pressing thediaphragm 89 to the atmospheric pressure chamber side and arranged to beadjusted in its pressing force by an adjusting screw 96. The negativepressure chamber 88 in the pressure change-over valve assembly 41 isconnected to a part of the suction pipe 2 adjacent the throttle valve 6through a conduit 98 provided with a solenoid valve 97. Thus, whennegative pressure in the negative pressure chamber 88 in said pressurechange-over valve assembly 41 is elevated, positive pressure in thepressure amplifier unit 11 is supplied to control valve 7, while whensaid negative pressure is reduced, negative pressure in the suction pipe2 is supplied to said control valve 7. The solenoid valve 97 functionsto selectively supply negative pressure in the suction pipe 2 oratmospheric pressure into the negative pressure chamber 88 in thepressure change-over valve assembly 41. The solenoid valve 97 comprisesa magnet coil 99 and a valve body 100 actuated by said magnet coil 99which receives a control signal from a control device 101 correspondingto the engine speed, atmospheric temperature and other factors.

Let us now see the operation of the just described exhaust gasrecirculation system of the present invention in a situation where thesolenoid valve 97 connects the pressure change-over valve 41 with thesuction pipe 2 and the engine is in a cranking, idling, decelerated orhigh-loaded state. Under such operating condition, negative pressure inthe neighborhood of and adjacent the throttle valve 6 is weak and suchnegative pressure is introduced into the negative pressure chamber 88 inthe pressure change-over valve assembly 41 through conduit 98 and actsweakly on the diaphragm 89, so that the valve seat 83 closes the valve92 under the stronger force of spring 95 thereby communicating conduit85 with conduit 71. Consequently, negative pressure in the suction pipe2 is introduced into the controlled pressure chamber 56 in the controlvalve assembly 7 through conduit 85, pressure change-over valve 41 andconduit 71, and a face pressure equivalent to the difference ineffective area between the diaphragms 58 and 59 works in the samedirection as the pressing force of spring 62, closing the fixed orifice54 with the valve 53. Therefore regardless of the pressure in thecontrolled pressure chamber 17 in the pressure amplifier unit 11, thevalve seat 83 in the pressure change-over valve assembly 41 stays closedby the valve 92 to inhibit supply of said pressure to the control valve7, so that no exhaust gas is recirculated from the exhaust manifold 3back into the intake manifold 2.

When the operating pattern of the engine is changed into an acceleratedor constant-speed operation, negative pressure around and adjacent thethrottle valve 6 is intensified and such intensified negative pressureis introduced into the negative pressure chamber 88 in the pressurechange-over valve assembly 41 through conduit 98 to press the diaphragm89 against the force of spring 95 to close the valve seat 84 with thevalve 92, thus communicating the controlled pressure chamber 17 in thepressure amplifier unit 11 with the conduit 71. During this time sincenegative pressure around the venturi 5 is being introduced into thenegative pressure chamber 35 in the pressure time, unit 11 and alsopositive pressure in the controlled pressure chamber 17 is beingamplified proportional to the change of negative pressure as said above,the controlled strong positive pressure in the controlled pressurechamber 17 is ggided into the controlled pressure chamber 56 in thecontrol valve assembly 7 through pressure change-over valve 41 andconduit 71, and hence a face pressure corresponding to the difference ineffective area between the diaphragms 58 and 59 works against thepressing force of spring 62, opening the fixed orifice 54 with the valve53. Therefore, exhaust gas is recirculated from the exhaust manifold 3into the intake manifold 2 through the control valve 7. As the variationof negative pressure in the suction pipe 2 conforms to the runningcondition of the engine, the exhaust gas recirculation rate alsoconforms to the operating pattern of the engine. During this period, nonegative pressure in the intake manifold 2 is introduced into thecontrol valve 7 as the valve seat 84 is closed by the valve 92 in thepressure change-over valve assembly 41.

When the engine operation is under the conditions other than above-said,that is, when the factors such as engine speed, engine cooling watertemperature, atmospheric temperature and vehicle speed are in a statewhere recirculation of exhaust gas is not required, the control device101 operates to transmit a signal to the magnet coil 99 of the solenoidvalve 97 to switch the solenoid valve 97 to communicate the negativepressure chamber 88 in the pressure change-over valve assembly 41 withthe atmosphere, so that the valve seat 83 in said valve assembly 41 isclosed by the valve 92 which is pressed by spring 95 through diaphragm89 and shaft 93. Thus, the pressure change-over valve 41 alwayscommunicates the control valve 7 and suction pipe 2, keeping the fixedorifice 54in the control valve 7 closed by the valve 53, and hence noexhaust gas is recirculated into the intake manifold 2.

Referring now to FIGS. 5 to 7, there is shown another embodiment of thepresent invention. This embodiment difiers from the preceding one inthat the pressure amplifier unit 11 is formed integral with the controlvalve assembly 7 and the pressure change-over valve assembly 41 isseparated therefrom. The route for communication of the intake manifold2, pressure change-over valve 41, pressure amplifier unit 11, air pump21, control valve 7 and solenoid valve 97 is same as in the precedingembodiment. Both embodiments are also identical in the manner in whichnegative pressure in the intake manifold 2 is amplified by the pressureamplifier unit 11 and the control valve 7 is opened by the action of theamplified positive pressure. In the drawings, the parts which are thesame as those in the preceding embodiment are assigned the samereference numerals. The pressure amplifier unit 11, as in the foregoingembodiment, has formed therein a negative pressure chamber 35, anatmospheric pressure chamber 18, a controlled pressure chamber 17 and anair bleeding section 26'. The controlled pressure chamber 17 doubles asthe controlled pressure chamber 56 for the control valve 7, and at apart of the air bleeding portion 26 opposed to said controlled pressurechamber 17 is provided a check valve 102 adapted for allowing release ofonly positive pressure from the controlled pressure chamber 17 into thebleeding hole 27'. The openingclosing valve 53 in the control valveassembly 7 is connected to a diaphragm 65' through a shaft 64 extendingthrough seal 63 in the valve body 51 and further to a lower part of theair bleeding portion 26 so that said valve 53 will be opened and closedin accordance with the behavior of the diaphragms l5 and 32. Thepressure change-over valve assembly 41 is separate from the pressureamplifier unit 1 1. It has a valve 92 adapted for selectively closingthe valve seats 83 and 84 and a negative pressure chamber 88 operable toswitch the valve 92. Conduit connecting to the suction pipe 2 andconduit 22 leading into the air pump 21 are selectively connected withthe controlled pressure chamber l7 in the pressure amplifier unit 11.

In the above-described mechanism, as in the preceding embodiment, thepressure amplifier unit 11 performs an amplifying operation torecirculate exhaust gas in the exhaust pipe into the intake manifold 2,but when positive pressure in the air pump 21 is introduced into thecontrolled pressure chamber 17 in said unit 1 1 through change-overvalve 41, a pertinent amount of positive pressure is released into theatmosphere from the bleeding hole 27 through check valve 102 so thatpositive pressure in the controlled pressure chamber 17 will become sameas produced by amplifying variation of negative pressure around theventuri 5, thus opening the fixed orifice 54 by the operating valve 53in' the control valve assembly 7. However, when negative pressure in thedownstream of the throttle valve 6 is introduced into the controlledpressure chamber 17 in the amplifier unit 11 through change-over valve41, the controlled pressure chamber 17' develops a negative pressure asno air is flown into said chamber 17 from the bleeding hole 27 throughcheck valve 102, so that the fixed orifice 54 is closed by the valve 53in the control valve assembly 7.

According to the present invention, as described above, the negativepressure in the suction pipe representing the operating condition of theengine is amplified into a positive pressure proportional to theabsolute value of the negative pressure by a pressure amplifier unitconsisting of two pieces of diaphragms and an air bleeding mechanism,and such positive pressure is introduced into a controlled pressurechamber in the control valve assembly which controls the exhaust gasrecirculation rate, thus allowing opening of the control valve with alarge positive pressure while controlling the exhaust gas recirculationrate corresponding to the operating condition of the engine. No problemis posed in the opening of the control valve even when using a springwith a strong pressing force in the control valve closing direction.Also, when it is desired to close the control valve in a certainoperating condition of the engine, negative pressure in the intakemanifold is introduced into the controlled pressure chamber in saidcontrol valve so that closing of the control valve is secured by suchnegative pressure and the force of the spring. Further, exhaust gasrecirculation is automatically stopped when the engine operation isunder other conditions where recirculation of exhaust gas is notrequired. Also, though compressed air in the controlled 40 pressurechamber in the pressure amplifier unit is released into the atmospherefrom the air bleeding portion, no problem arises in such matter as theair pump of the pressure source is of a sufficiently large capacity.

What we claim is:

1. An exhaust gas recirculation system for an internal combustion enginein which the exhaust and suction systems are communicated with eachother by a conduit provided with a control valve, characterized in thatsaid control valve is opened or closed by a pressure amplifying unit soas to recirculate exhaust gas into the suction system corresponding tovariation of negative pressure in the suction system, said pressureamplifying unit comprising a first diaphragm and a second diaphragmarranged to divide the interior of the housing into three chambers, afirst chamber defined by said first diaphragm so that compressed airwill be introduced thereinto from a pressure source, said first chamberhaving a pressure outlet portion, a second chamber defined between saidfirst and second diaphragms and communicated with the atmosphere, athird chamber defined by said second diaphragm so that negative pressureadjacent a venturi in the suction system will be introduced thereinto, avalve mounted on said first diaphragm to control communication betweensaid first and second chambers, and an operating member mounted on saidsecond diaphragm to operate said valve.

2. The exhaust gas recirculation system as set forth in claim 1, furtherincluding a pressure switch-over valve by which a pressure outlet portin the pressure amplifying unit and a part of the suction system locateddownstream of a throttle valve are selectively communicated with thecontrolled pressure chamber in said control valve, said pressureswitch-over valve having a negative pressure chamber communicating witha part of the suction system located adjacent the throttle valve.

3. The exhaust gas recirculation system as set forth in claim 2, furtherincluding a valve means provided in a conduit communicating the negativepressure chamber in the pressure switch-over valve with a part of thesuction system adjacent the throttle valve, said valve means beingadapted to operate corresponding to the operating condition of theengine and whereby communication between said negative pressure chamberin the pressure switch-over valve and the suction system is shut offwhen recirculation of exhaust gas is not required.

1. An exhaust gas recirculation system for an interNal combustion enginein which the exhaust and suction systems are communicated with eachother by a conduit provided with a control valve, characterized in thatsaid control valve is opened or closed by a pressure amplifying unit soas to recirculate exhaust gas into the suction system corresponding tovariation of negative pressure in the suction system, said pressureamplifying unit comprising a first diaphragm and a second diaphragmarranged to divide the interior of the housing into three chambers, afirst chamber defined by said first diaphragm so that compressed airwill be introduced thereinto from a pressure source, said first chamberhaving a pressure outlet portion, a second chamber defined between saidfirst and second diaphragms and communicated with the atmosphere, athird chamber defined by said second diaphragm so that negative pressureadjacent a venturi in the suction system will be introduced thereinto, avalve mounted on said first diaphragm to control communication betweensaid first and second chambers, and an operating member mounted on saidsecond diaphragm to operate said valve.
 2. The exhaust gas recirculationsystem as set forth in claim 1, further including a pressure switch-overvalve by which a pressure outlet port in the pressure amplifying unitand a part of the suction system located downstream of a throttle valveare selectively communicated with the controlled pressure chamber insaid control valve, said pressure switch-over valve having a negativepressure chamber communicating with a part of the suction system locatedadjacent the throttle valve.
 3. The exhaust gas recirculation system asset forth in claim 2, further including a valve means provided in aconduit communicating the negative pressure chamber in the pressureswitch-over valve with a part of the suction system adjacent thethrottle valve, said valve means being adapted to operate correspondingto the operating condition of the engine and whereby communicationbetween said negative pressure chamber in the pressure switch-over valveand the suction system is shut off when recirculation of exhaust gas isnot required.